Lasers Could Replace Quartz in Future Electronics

Developed by a team at the California Institute of Technology, the new method can stabilize microwave signals in the gigahertz range using two laser beams as the reference.

Quartz crystals have traditionally been used as the tuning reference for oscillators in electronic devices, specifically those that fall at or below the megahertz range.

A new laser-based frequency reference (left) could replace the traditional quartz crystal reference (center) in future electronic devices. Courtesy of Jiang Li/Caltech.
An electrical frequency division technique, which converts higher-frequency microwave signals into lower-frequency signals that the crystals stabilize, has also been a part of the process.

However, advances in technology and the future of consumer electronics will require tuning references for higher frequencies, the researchers said.

The new technique, called electro-optical frequency division, essentially reverses the architecture used in standard crystal-stabilized microwave oscillators.

“The quartz reference is replaced by optical signals much higher in frequency than the microwave signal to be stabilized,” said Dr. Kerry Vahala, a professor of information science and technology and applied physics at Caltech.

Frequency dividers typically used in electronics work at frequencies less than 50 to 100 GHz. The new divider method stabilizes signals at much higher frequencies, according to CalTech postdoctoral scholar Jiang Li. He likened it to a bicycle gear chain “that translates pedaling motion from a small, fast-moving gear into the motion of a much larger wheel.”

The optical reference used in the study is a laser that is 6 mm in diameter, which the researchers said is small enough to be effective with compact photonic devices.

“There are always trade-offs between the highest performance, the smallest size, and the best ease of integration,” Vahala said. “But even in this first demonstration, these optical oscillators have many advantages. They are on par with, and in some cases even better than, what is available with widespread electronic technology.”

The work was funded by DARPA, the Caltech Institute for Quantum Information and Matter, the National Science Foundation’s Physics Frontiers Center and the Caltech Kavli NanoScience Institute.